The present invention relates generally to an impact printer, and, in particular, to a printer provided with an improved impact dot head.
Reference is first made to FIGS. 1 and 2 of the drawings to describe a conventional impact printer construction. Referring specifically to FIG. 1, conventional impact dot head printers have a wire arrangement as depicted therein. The print head includes a plurality of printing wires 308 coupled respectively to armatures 319 which drive the wires. Printing wires 308 and armatures 319 are arranged in a circular array at equally spaced intervals. Further, the printing tips of the wires are arranged in a linear matrix array. In FIG. 2, each armature 319 is maintained in a waiting or rest state by means of a spring force provided from a restoring coil spring 316. Printer wire 308 is supported by a plurality of wire guides 307 in an untensioned (i.e., relaxed) state.
The construction of such a conventional printer establishes a different bending .DELTA.Y of each printing wire 308 as depicted in FIGS. 1 and 2. In this manner, a bending moment M of printing wire 308 differs for each armature 319. Further, the bending moment M develops a distinct rotational force for each armature. Accordingly, the retaining force or restoring force produced during the waiting state of armature 319 equals the sum of the spring force developed by the restoring spring and the force created by rotating the armature developed from the bending moment M of printing wire 308. Therefore, the spring force of the restoring spring is equal with respect to each armature. However, the retaining force differs for each armature causing different printing impact for each armature and therefore making uniform printing quality unattainable.
To overcome these problems, the prior art has changed the setting angle of printing wire 308 with respect to each armature to obtain a uniform restoring force. In addition, a method has been disclosed to change the restoring spring of each armature to obtain a uniform restoring force. Such a system is disclosed, for example, in Japanese Patent Laid-Open No. 152870/84 dated Feb. 19, 1983. However, the above arrangements have failed to create uniform printing from an impact dot head and increased performance while increasing the number of parts and the associated assembly cost.
Accordingly, it is desired to provide an improved impact dot head for a printer which increases the performance of the printer by producing a uniform printing quality obtained without increasing the assembling cost or the number of parts.